1. Field
The present patent application generally relates to a method and/or apparatus for multicolor image forming. For example, at least one embodiment of the present patent application relates to an image forming apparatus, for example, a color copier and a color printer, for effectively adjusting phase differences of a plurality of image bearing members included in the image forming apparatus to reduce color shift caused by position shifts of the image bearing members.
2. Discussion of the Related Art
In an image forming apparatus using a plurality of image bearing members, a deviation caused by the fluctuation of a rotational speed of each image bearing member arises from tooth profile error of an image bearing member drive gear or an eccentricity of the image bearing member in mounting to the image forming apparatus, which contributes to color shifts when forming an overlaid image.
A well known technique for reducing color shifts of the image bearing member includes a method of matching a period of the fluctuation of a rotational speed of each image bearing member to minimize the amount of color shift so that an image having high quality can be produced.
To adjust the period of the fluctuation in the rotational speed of each image bearing member, there are some techniques, for example, proposed in Japanese Patent Laid-Open Application Publication Nos. 09-146329 and 2001-305820, that a pattern detecting part detects a color shift calibration pattern image formed by each of image bearing members to obtain a speed fluctuation period of each image bearing member and an amount of fluctuation of the rotational speed. Based on the speed fluctuation period and the amount of fluctuation of the rotational speed, a motor control part adjusts and controls the drive speed of a motor to detect phase differences between the image bearing members by the pattern detecting part. The information of the phase differences is stored as a profile into a volatile memory and is used to adjust phases between the image bearing members before image forming operations.
In this case, however, the amount of rotational speed deviation is obtained based on the speed fluctuation period by adding the speed fluctuation of an image bearing member drive gear to the speed fluctuation of the image bearing member. Therefore, the waveform of speed fluctuation of each image bearing member differs from each other according to the condition of engagement of the image bearing member drive gear and the image bearing member that have the same rotation period. Since the image bearing member is a consumable and is replaced on a regular basis by a user, it is difficult to tell how the user engages the image bearing member with the image bearing member drive gear during maintenance and/or replacement of the image bearing member.
Further, there is another technique, for example, proposed in Japanese Patent Laid-Open Application Publication No. 2003-233235, that utilized in a color image forming apparatus that includes a pattern forming unit, a rotational phase detecting unit, a phase adjusting unit, and a phase information storing unit. In the color image forming apparatus, the pattern forming unit forms a positional deviation detecting pattern on a carrying member. The rotational phase detecting unit adjusts the rotational phase of a detection color at every prescribed angle with reference to a reference color in the positional deviation detecting pattern formed on the carrying member so that the reference color and the detection color can be simultaneously detected, and then, calculates the positional deviation of the detection color from the reference-color and the optimum rotational phase of the uneven angular velocity of the image bearing member required to reduce the positional deviation to the minimum. The phase adjusting unit adjusts the rotational phase.
The phase information storing unit stores the rotational phase information determined by the rotational phase detecting unit. Then, the rotational phase is adjusted by the rotational phase detecting unit so that the positional deviation may become the minimum. The determined rotational phase information is stored at a manufacturing stage before the delivery from the factory.
Further, there is another technique, for example, proposed in Japanese Patent Laid-Open Application Publication No. 2005-017768, that is in a multi-color image forming apparatus equipped with a plurality of image stations, a plurality of exposing devices, and a control unit. The plurality of image stations include an image carrier, a plurality of image bearing members to be brought into contact with the image carrier at the time of image formation to a recording medium, and a toner developing device which elicits latent images formed on the image bearing members as toner images. The plurality of exposing devices irradiates light to each of the image bearing member and forms the latent image.
The control unit performs control of adjusting phase difference between the respective image bearing members. The control unit includes an electrostatic latent image measurement unit for measuring the latent images formed on the respective image bearing members, a rotational fluctuation measurement unit for measuring rotational fluctuation of the respective image bearing members based on a detection result detected by the electrostatic latent image measurement unit, and a phase difference measurement unit for measuring the phase difference between the respective image bearing member based on a measurement result measured by the rotational fluctuation measurement unit. With the above-described structure, rotational speed of the image bearing members is changed based on a detection result detected by the phase difference measurement unit.